EP0232131A2 - Plate-like barium ferrite particles suitable for use in magnetic recording and process for producing the same - Google Patents
Plate-like barium ferrite particles suitable for use in magnetic recording and process for producing the same Download PDFInfo
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- EP0232131A2 EP0232131A2 EP87300779A EP87300779A EP0232131A2 EP 0232131 A2 EP0232131 A2 EP 0232131A2 EP 87300779 A EP87300779 A EP 87300779A EP 87300779 A EP87300779 A EP 87300779A EP 0232131 A2 EP0232131 A2 EP 0232131A2
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- European Patent Office
- Prior art keywords
- plate
- barium ferrite
- zinc
- ferrite particles
- particles
- Prior art date
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- 239000002245 particle Substances 0.000 title claims abstract description 197
- AJCDFVKYMIUXCR-UHFFFAOYSA-N oxobarium;oxo(oxoferriooxy)iron Chemical compound [Ba]=O.O=[Fe]O[Fe]=O.O=[Fe]O[Fe]=O.O=[Fe]O[Fe]=O.O=[Fe]O[Fe]=O.O=[Fe]O[Fe]=O.O=[Fe]O[Fe]=O AJCDFVKYMIUXCR-UHFFFAOYSA-N 0.000 title claims abstract description 115
- 230000005291 magnetic effect Effects 0.000 title claims abstract description 36
- 238000000034 method Methods 0.000 title claims description 37
- 239000011701 zinc Substances 0.000 claims abstract description 53
- 229910052725 zinc Inorganic materials 0.000 claims abstract description 50
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims abstract description 49
- 230000005415 magnetization Effects 0.000 claims abstract description 48
- 239000006104 solid solution Substances 0.000 claims abstract description 28
- VTLYFUHAOXGGBS-UHFFFAOYSA-N Fe3+ Chemical compound [Fe+3] VTLYFUHAOXGGBS-UHFFFAOYSA-N 0.000 claims abstract description 26
- 229910052719 titanium Inorganic materials 0.000 claims description 19
- UGZADUVQMDAIAO-UHFFFAOYSA-L zinc hydroxide Chemical compound [OH-].[OH-].[Zn+2] UGZADUVQMDAIAO-UHFFFAOYSA-L 0.000 claims description 18
- 229910021511 zinc hydroxide Inorganic materials 0.000 claims description 18
- 229940007718 zinc hydroxide Drugs 0.000 claims description 18
- 239000007864 aqueous solution Substances 0.000 claims description 15
- 239000000725 suspension Substances 0.000 claims description 12
- 229910001422 barium ion Inorganic materials 0.000 claims description 9
- XLJKHNWPARRRJB-UHFFFAOYSA-N cobalt(2+) Chemical compound [Co+2] XLJKHNWPARRRJB-UHFFFAOYSA-N 0.000 claims description 9
- JIAARYAFYJHUJI-UHFFFAOYSA-L zinc dichloride Chemical compound [Cl-].[Cl-].[Zn+2] JIAARYAFYJHUJI-UHFFFAOYSA-L 0.000 claims description 8
- 238000001035 drying Methods 0.000 claims description 5
- 238000001914 filtration Methods 0.000 claims description 5
- VNDYJBBGRKZCSX-UHFFFAOYSA-L zinc bromide Chemical compound Br[Zn]Br VNDYJBBGRKZCSX-UHFFFAOYSA-L 0.000 claims description 4
- 239000011592 zinc chloride Substances 0.000 claims description 4
- 235000005074 zinc chloride Nutrition 0.000 claims description 4
- 239000005083 Zinc sulfide Substances 0.000 claims description 2
- ZOIORXHNWRGPMV-UHFFFAOYSA-N acetic acid;zinc Chemical compound [Zn].CC(O)=O.CC(O)=O ZOIORXHNWRGPMV-UHFFFAOYSA-N 0.000 claims description 2
- 239000004246 zinc acetate Substances 0.000 claims description 2
- AKJVMGQSGCSQBU-UHFFFAOYSA-N zinc azanidylidenezinc Chemical compound [Zn++].[N-]=[Zn].[N-]=[Zn] AKJVMGQSGCSQBU-UHFFFAOYSA-N 0.000 claims description 2
- 229940102001 zinc bromide Drugs 0.000 claims description 2
- 229910052984 zinc sulfide Inorganic materials 0.000 claims description 2
- DRDVZXDWVBGGMH-UHFFFAOYSA-N zinc;sulfide Chemical compound [S-2].[Zn+2] DRDVZXDWVBGGMH-UHFFFAOYSA-N 0.000 claims description 2
- PTFCDOFLOPIGGS-UHFFFAOYSA-N Zinc dication Chemical compound [Zn+2] PTFCDOFLOPIGGS-UHFFFAOYSA-N 0.000 claims 3
- MSNWSDPPULHLDL-UHFFFAOYSA-K ferric hydroxide Chemical compound [OH-].[OH-].[OH-].[Fe+3] MSNWSDPPULHLDL-UHFFFAOYSA-K 0.000 claims 1
- 239000010936 titanium Substances 0.000 description 63
- 150000001875 compounds Chemical class 0.000 description 21
- 230000000052 comparative effect Effects 0.000 description 14
- 238000004458 analytical method Methods 0.000 description 13
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 9
- 238000004876 x-ray fluorescence Methods 0.000 description 9
- 230000005294 ferromagnetic effect Effects 0.000 description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 7
- 239000000463 material Substances 0.000 description 7
- 238000000635 electron micrograph Methods 0.000 description 6
- NCNCGGDMXMBVIA-UHFFFAOYSA-L iron(ii) hydroxide Chemical compound [OH-].[OH-].[Fe+2] NCNCGGDMXMBVIA-UHFFFAOYSA-L 0.000 description 6
- -1 Fe(III) ions Chemical class 0.000 description 5
- 238000000151 deposition Methods 0.000 description 5
- 238000010438 heat treatment Methods 0.000 description 5
- 235000014413 iron hydroxide Nutrition 0.000 description 5
- 239000007858 starting material Substances 0.000 description 5
- 238000002441 X-ray diffraction Methods 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 239000002244 precipitate Substances 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 229910000859 α-Fe Inorganic materials 0.000 description 4
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 239000012670 alkaline solution Substances 0.000 description 3
- 230000008021 deposition Effects 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000005245 sintering Methods 0.000 description 3
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 2
- 150000008044 alkali metal hydroxides Chemical class 0.000 description 2
- RQPZNWPYLFFXCP-UHFFFAOYSA-L barium dihydroxide Chemical compound [OH-].[OH-].[Ba+2] RQPZNWPYLFFXCP-UHFFFAOYSA-L 0.000 description 2
- 239000003638 chemical reducing agent Substances 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 238000000576 coating method Methods 0.000 description 2
- UFMZWBIQTDUYBN-UHFFFAOYSA-N cobalt dinitrate Chemical compound [Co+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O UFMZWBIQTDUYBN-UHFFFAOYSA-N 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 239000000696 magnetic material Substances 0.000 description 2
- 239000006249 magnetic particle Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 150000003839 salts Chemical class 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- XJDNKRIXUMDJCW-UHFFFAOYSA-J titanium tetrachloride Chemical compound Cl[Ti](Cl)(Cl)Cl XJDNKRIXUMDJCW-UHFFFAOYSA-J 0.000 description 2
- UAYWVJHJZHQCIE-UHFFFAOYSA-L zinc iodide Chemical compound I[Zn]I UAYWVJHJZHQCIE-UHFFFAOYSA-L 0.000 description 2
- 238000004438 BET method Methods 0.000 description 1
- 229910003074 TiCl4 Inorganic materials 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 229910052788 barium Inorganic materials 0.000 description 1
- WDIHJSXYQDMJHN-UHFFFAOYSA-L barium chloride Chemical compound [Cl-].[Cl-].[Ba+2] WDIHJSXYQDMJHN-UHFFFAOYSA-L 0.000 description 1
- 229910001626 barium chloride Inorganic materials 0.000 description 1
- 229910001863 barium hydroxide Inorganic materials 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GVPFVAHMJGGAJG-UHFFFAOYSA-L cobalt dichloride Chemical compound [Cl-].[Cl-].[Co+2] GVPFVAHMJGGAJG-UHFFFAOYSA-L 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000007499 fusion processing Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 238000007496 glass forming Methods 0.000 description 1
- 150000004820 halides Chemical class 0.000 description 1
- FBAFATDZDUQKNH-UHFFFAOYSA-M iron chloride Chemical compound [Cl-].[Fe] FBAFATDZDUQKNH-UHFFFAOYSA-M 0.000 description 1
- 229910001337 iron nitride Inorganic materials 0.000 description 1
- VCJMYUPGQJHHFU-UHFFFAOYSA-N iron(III) nitrate Inorganic materials [Fe+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VCJMYUPGQJHHFU-UHFFFAOYSA-N 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- SESRATMNYRWUTR-UHFFFAOYSA-N sulfinyltitanium Chemical compound [Ti].S=O SESRATMNYRWUTR-UHFFFAOYSA-N 0.000 description 1
- 150000003752 zinc compounds Chemical class 0.000 description 1
- 239000011787 zinc oxide Substances 0.000 description 1
Images
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/10—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials non-metallic substances, e.g. ferrites, e.g. [(Ba,Sr)O(Fe2O3)6] ferrites with hexagonal structure
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/62—Record carriers characterised by the selection of the material
- G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
- G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
- G11B5/706—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material
- G11B5/70626—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material containing non-metallic substances
- G11B5/70642—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the composition of the magnetic material containing non-metallic substances iron oxides
- G11B5/70678—Ferrites
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S428/00—Stock material or miscellaneous articles
- Y10S428/90—Magnetic feature
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/29—Coated or structually defined flake, particle, cell, strand, strand portion, rod, filament, macroscopic fiber or mass thereof
- Y10T428/2982—Particulate matter [e.g., sphere, flake, etc.]
- Y10T428/2991—Coated
Definitions
- the present invention relates to plate-like barium ferrite particles suitable for use in magnetic recording and to a process for producing the same.
- barium ferrite particles are known as ferromagnetic non-acicular particles.
- magneto plumbite ferrite which is used as a magnetic recording material is required to have the greatest possible saturation magnetization .
- a coercive force of about 300 to 1,500 Oe is generally required, and in order to reduce the coercive force of the produced barium ferrite particles to an appropriate coercive force in the autoclaving process, a method of substituting a part of Fe(III) in ferrite by Ti(IV) and Co(II), or Co(II) and d tivalent metal ions M(II) of Mn, Zn, Ni or the like has been proposed.
- EP-A-0123445 discloses "plate-like barium ferrite particles which are represented by the formula BaCo x Ti y Fe 12-x-y O 19 wherein x and y independently are numbers from 0.1 to 0.5 and which have a BET specific surface area of from 20 to 70 m 2 /g, an average particle diameter of from 0.05 to 0.3 ⁇ m, a magnetization of larger than 30 emu/g in a magnetic field of 7.96 x 10 5 A m -1 (10 KOe) and a coercive force of from 2.39 x 10 4 to 7 .
- 96 x 10 4 A m -1 300 to 1,000 Oe
- the particle size of plate-like barium ferrite particles for use in magnetic recording is required to be as fine as possible, in particular, to be not greater than 0.3 ⁇ m.
- the crystalline particle diameter of the ferrite is preferably substantially less than 0.3 ⁇ m.
- the particle diameter is about 0.01 ⁇ m, the desired coercive force is not exhibited. Therefore, a crystalline particle diameter of 0.01 to 0.3 ⁇ m is appropriate.
- the magnetic particle is as fine as possible and the BET specific surface area is large.
- FIG. 3 shows the relationship between the particle size as well as BET specific surface area and noise level of the particles in acicular maghemite particles with Co deposition.
- Plate-like barium ferrite particles having a large magnetization, an appropriate coercive force, an appropriate particle size and a large BET specific surface area have now been strongly demanded, but it is difficult to obtain plate-like barium ferrite particles having both large BET specific surface area and large magnetization because the magnetization of plate-like barium ferrite particles generally have a tendency to be reduced with the increase in the BET specific surface area.
- the plate-like barium ferrite particles described in the Synopses of the Lectures in 7-th Meeting of the Magnetics Society of Japan and Japanese Patent Application Laying-Open (KOKAI) No. 60-66321 (1985) are obtained by mixing a barium ferrite material with a glass forming material, melting the thus obtained mixture, and rapidly cooling the melt, namely by a so- called glass fusion process.
- a similar relationship between the BET specific surface area and the magnetization is found with plate-like barium ferrite particles produced by autoclaving.
- the magnetization tends to increase with the rise in baking temperature, and a high temperature of more than 900°C is required in order to obtain a large magnetization, in particular, a magnetization of not less than 57 emu/g, preferably not less than 60 emu/g.
- a high temperature of more than 900°C is required in order to obtain a large magnetization, in particular, a magnetization of not less than 57 emu/g, preferably not less than 60 emu/g.
- sintering between the particles is so marked as to bulk, these formed bulk particles being unfavorable as magnetic particles for use in magnetic recording.
- plate-like barium ferrite particles having a large B ET specific surface area, a large magnetization and an average particle size of less than 0.1 ⁇ m by autoclaving it has been found that plate-like barium ferrite particles having a BET specific surface area of not less than 55 m 2 /g, a magnetization (M) of not less than 57 emu/g, preferably not less than 60 emu/g and a coercive force (Hc) of 300 to 1,500 Oe by suspending plate-like barium ferrite particles containing Co and Ti, the atomic ratio of Co to Fe(III) being from 0.02 : 1 to 0.13 : 1 and the molar ratio of Ti to Co being from more than 0 to not more than 0.8, in an aqueous solution containing zinc of pH 4.0 to 12.0 to obtain the plate-like barium ferrite particles deposited with the zinc hydroxide on the surfaces thereof, filtering out and drying the particles,
- plate-like barium ferrite particles with a solid solution of zinc on the surface thereof which have an average particle diameter of not less than 0.03 ⁇ m and less than 0.1 ⁇ m, a BET specific surface area of 55 to 80 m 2 /g, a coercive force of 300 to 1,500 Oe and a magnetization of not less than 57 emu/g in magnetic field of 10 KOe, and which are represented by the following formula (I): wherein x and y are independently from 0.02 to 0.12 and n is from 4 to 11, the atomic ratio of Co to Fe(III) being from 0.02:1 to 0.13 : 1 and the molar ratio of Ti to Co being from more than 0 to not more than 0.8.
- a process for producing plate-like barium ferrite particles with a solid solution of zinc on the surface thereof which are represented by the following formula (I): wherein x and y are independently from 0.02 to 0.12 and n is from 4 to 11, the atomic ratio of Co to Fe(III) being from 0.02 :1 to 0.13 : 1 and the molar ratio of Ti to Co being from more than 0 to not more than 0.8, which comprises autoclaving at a temperature of from 120 to 330°C an aqueous alkaline suspension of iron hydroxide containing Co(II), Ti(IV) and Ba ions and a molar excess with respect to the total amount of Fe(III), Co(II), Ti(IV) and Ba ions of an alkali metal hydroxide, in said suspension the atomic ratio of the amount of Co to the amount of Fe(III) being from 0.02 : 1 to 0.13 : 1 and the molar ratio of Ti to Co being from more than
- Plate-like barium ferrite particles suitable for use in magnetic recording according to the present invention which have an average particle diameter of not less than 0.03 ⁇ m and less than 0.1 ⁇ m, a BET specific surface area of 55 to 80 m 2 /g, a coercive force of 300 to 1,500 Oe and a magnetization of not less than 57 emu/g, preferably not less than 60 emu/g, in a magnetic field of 10 KOe, and which are represented by the following formula (I): wherein x and y are independently from 0.02 to 0.12 and n is from 4 to 11, the atomic ratio of Co to Fe(III) being from 0.02 : 1 to 0.13 : 1 and the molar ratio of Ti to Co being from more than 0 to not more than 0.8, and on which the surface thereof a solid solution of zinc is formed, are obtained by the following process.
- the plate-like barium ferrite particles containing Co and Ti are first produced by adding 2 to 13 atom% of Co compound with respect to Fe(III) and a Ti compound in a molar ratio of 0 ⁇ Ti/Co ⁇ 0.8 to an aqueous alkaline suspension of iron hydroxide (III) containing Ba ions, and autoclaving the thus obtained aqueous alkaline suspension of iron hydroxide (III) at a temperature ranging from 120 to 330°C.
- the thus obtained plate-like barium ferrite particles containing Co and Ti is suspended in an aqueous solution containing zinc of pH 4.0 to 12.0 to deposit the zinc hydroxide on the surface of the plate-like barium ferrite particles containing Co and Ti, and after filtering out and drying, the thus obtained plate-like barium ferrite particles are baked at a temperature of 600 to 900°C.
- the heart of the present invention is characterized in that plate-like barium ferrite particles having an average particle diameter of less than 0.1 um can be produced by adding 2 to 13 atom% of Co compound with respect to Fe(III) and a Ti compound in a molar ratio of 0 ⁇ Ti/Co s 0.8 to an aqueous alkaline suspension of iron hydroxide (III), and autoclaving the aqueous alkaline suspension of iron hydroxide (III) at a temperature of 120 to 330°C; the plate-like barium ferrite particles containing Co and Ti are suspended in an aqueous solution containing zinc of pH 4.0 to 12.0, thereby obtaining plate-like barium ferrite particles containing Co and Ti, on which the surface thereof the zinc hydroxide is deposited; and after filtering out and drying, the thus obtained plate-like barium ferrite particles containing Co and Ti are baked at a temperature of 600 to 900°C to form a solid solution of zinc on the surface thereof, thereby enabling the magnet
- Figs. 1 and 2 show the relationship between the ratio of addition (in a molar ratio) of Ti with respect to Co in the case of adding 7.86 atom% of Co to Fe (III), and the particle size and the B E T specific surface area, respectively, of the produced plate-like barium ferrite particles.
- a method of adding a Co compound and a Ti compound when producing plate-like barium ferrite particles by autoclaving is conventionally known, as is disclosed in, e.g., Japanese Patent Application Laying-Open (KOKAI) No. 56-149328(1981).
- the purpose of this method is-to reduce a coercive force by adjusting the valence of Fe(III) ions and additives, and therefore it is preferable that the amounts of Co(II) compound and Ti(IV) compound to be added are equimolar.
- the amounts of Co(II) compound and Ti(IV) compound to be added are different and they are added in order to control the particle size and the BET specific surface area of produced plate-like barium ferrite particles. Accordingly, the process of the present invention is completely different from the conventional process in technical means, objects and effects.
- the magnetization effectively increases and the coercive force reduces.
- the amount of a solid solution of zinc on the surfaces of plate-like barium ferrite particles is controlled by adjusting the pH of the solution at the time of depositing the zinc hydroxide on the surface of the particles and the amount of zinc to be added.
- the amount of deposition of the zinc hydroxide on the surfaces of the particles has a tendency of increasing with the increase in pH, and preferable pH is in the range of 4 to 12 and more preferable pH is in the range of 8 to 10.
- Fe(III) salt in the present invention iron nitride, iron chloride, or the like may be used.
- Ba ions in the present invention barium hydroxide, barium chloride, barium nitride or the like may be used.
- the reaction temperature in autoclaving in the present invention is 120 to 330°C.
- the upper limit is determined to be 330°C in consideration of the safety of the apparatus.
- Co compound in the present invention cobalt chloride, cobalt nitride or the like may be used.
- the amount of the Co compound to be added is 2 to 13 atom% with respect to Fe(III).
- the Ti compound used in the present invention includes titanium chloride, titanium oxysulfide and alkali titanium.
- the amount of Ti compound to be added is in the range of 0 ⁇ Ti/Co ⁇ 0.8 in a molar ratio.
- the entire amount of Co compound and Ti compound to be added is contained in plate-like barium ferrite particles, and accordingly the plate-like barium ferrite particles obtained contains 2 to 13 atom%, preferably 4.0 to 10.0 atom% with respect to Fe, and Ti in the range of 0 ⁇ Ti/Co ⁇ 0.8, preferably 0.1 ⁇ Ti/Co ⁇ 0.7 in a molar ratio.
- the plate-like barium ferrite particles obtained in this way are represented by the formula: wherein n is 4 to 11, x and y are independently 0.02 to 0.12, 0 Co/Fe (atom%) being 2 to 13, preferably 4.t to 10, and Ti/Co (molar ratio) being more than 0 and not more than 0.8, preferably 0.1 to 0.7.
- the zinc hydroxide in the present invention is deposited by suspending plate-like barium ferrite particles in an aqueous solution containing zinc of pH 4.0 to 12.0, preferably pH 8 to 10.
- a halide such as zinc chloride, zinc bromide and zinc iodide; zinc nitride; zinc sulfide; zinc acetate or the like may be used.
- the baking temperature in the present invention is 600 to 900°C, preferably 700 to 850°C.
- the plate-like barium ferrite particles according to the present invention after baking have a BET specific surface area of 55 to 80 m 2 /g, a coercive force (Hc) of 300 to 1,500 Oe and a magnetization (M) of not less than 57 emu/g, preferably not less than 60 emu/g, in magnetic field of 10 KOe.
- the BET specific surface area is less than 55 m 2 /g, it is difficult to reduce noise in a magnetic recording medium, and if it is more than 80 m 2 /g, dispersion of the particles in a vehicle is difficult.
- the BET specific surface area is preferably 60 to 75 m 2 /g.
- the surfaces of the plate-like barium ferrite particles may be coated with a compound showing an anti-sintering effect such as an Si compound, At compound and P compound before baking.
- the amount of a solid solution of zinc with respect to plate-like barium ferrite particles of the present invention is 0.2 to 5.0 wt%, preferably 0.7 to 4.5 wt%.
- the plate-like barium ferrite particles with a solid solution of zinc on the surface thereof according to the present invention represented by the formula: wherein n is 4 to 11, x and y are independently 0.02 to 0.12, Co/Fe (atom%) being 2 to 13 and Ti/Co (molar ratio) being more than 0 and not more than 0.8, have an average particle diameter of not less than 0.03 ⁇ m and less than 0.1 ⁇ m, a BET specific surface area of 55 to 80 m 2 /g, preferably 60 to 75 m 2 /g, a magnetization (M) of not lower than 57 emu/g, preferably not less than 60 emu/g, in magnetic field of 10 KOe, and a coercive force (Hc) of 300 to 1,500 Oe, preferably 400 to 1,300 Oe, they are suitable as a magnetic material for magnetic recording, especially, as a perpendicular magnetic recording material.
- M magnetization
- Hc coercive force
- the average particle diameter and the specific surface area in each of the examples and comparative examples are represented by the values measured from an electron microphotograph and a BET method, respectively.
- the magnetization (M) and the coercive force (Hc) of the particles were measured in the form of powders in magnetic field of 10 KOe.
- Various plate-like barium ferrite particles were produced by the same process as that in Example 1 by varying the kinds of ferric salt aqueous solutions and Ba salt aqueous solutions, the kinds and quantities of Co compounds and Ti compounds, and reaction temperature and time.
- Brown ferromagnetic precipitates were generated in the same way as in Example 2 except that 0.98 mol of zinc chloride, as well as Co and Ti, was added in autoclaving. The precipitates were filtered out, adequately washed and dried.
- the brown ferromagnetic particles obtained in Example 1 were used as the starting material. 100 g of the starting material was dispersed and mixed in an aqueous solution containing 0.07 mol of zinc chloride, and after the zinc hydroxide was deposited on the surfaces of the particles when the pH of the solution was 6.0, the particles were filtered out, dried and then baked at 800°C for 2.0 hours.
- the particles obtained by baking had an average particle diameter of 0.04 ⁇ m and a BET specific surface area of 74.8 m 2 /g, as is clear from the electron microphotograph (x 100,000) in Fig. 4.
- a coercive force (Hc) was 710 Oe and a magnetization (M) was 63.9 emu/g.
- the plate-like barium ferrite particles were diffracted by an X-ray, only the peaks that represent a magneto plumbite structure were observed, as is clear from Fig. 5, and as a result of chemical analysis of the particles, no zinc oxide or zinc hydroxide was detected which is to be extracted with heating from an alkaline solution. From these facts it was confirmed that a solid solution of Zn had been formed on the surface of the particles. According to X-ray fluorescence analysis, the composition of the thus obtained plate-like barium ferrite particles with a solid solution of zinc is represented by BaO ⁇ 8.5[(Fe 0.909 Co 0.078 Ti 0.013 ) 2 O 2.94 ].
- Various plate-like barium ferrite particles were produced by the same process as that in Example 9 by varying the kinds of the starting material, and the kinds and quantities of Zn to be added, and heating temperature and time.
- Plate-like barium ferrite particles with a solid solution of zinc on the surface thereof were obtained by the same process as that in Example 9 except using the plate-like barium ferrite particles obtained in Comparative Example 1 as the starting material.
- the thus obtained particles by baking had an average particle diameter of 0.15 um and a BET specific surface area of 39.3 m 2 /g.
- a coercive force (Hc) was 1,290 Oe and a magnetization (M) was 59.1 emu/g.
- the particles contained 1.4 atom% of Co with respect to Fe and 0.5 atom% of Ti with respect to Co, and an amount of a solid solution of zinc thereof was 2.8 wt%.
- Plate-like barium ferrite particles were obtained by the same process as that in Example 13 except using the plate-like barium ferrite particles obtained in Comparative Example 2 as the starting material and depositing no zinc hydroxide.
- the thus obtained particles by baking had an average particle diameter of 0.10 pm and a BET specific surface area of 47. 0 m 2 /g.
- a coercive force (Hc) was 1,180 Oe and a magnetization (M) was 53.2 emu/g.
- the particles contained 8.6 atom% of Co with respect to Fe, 0.33 atom% of Ti with respect to Co, and 4.4 wt% of zinc.
- Plate-like barium ferrite particles were obtained by the : same process as that in Example 13 except that no zinc hydroxide was deposited on the plate-like barium ferrite particles containing Co and Ti and the baking temperature was 920°C.
- the thus obtained particles by baking had an average particle diameter of 0.18 ⁇ m and a BET specific surface area of 18.0 m 2 /g.
- a coercive force (Hc) was 1,086 Oe and a magnetization (M) was 57.0 emu/g.
- the particles contained 8.6 atom% of Co with respect to Fe and 0.33 atom% of Ti with respect to Co.
- Plate-like barium ferrite particles were obtained by the same process as that in Example 13 except that no zinc hydroxide was deposited on the plate-like barium ferrite particle.
- Zinc hydroxide was deposited on the plate-like barium ferrite particles in the same way as in Example 13. The thus obtained plate-like barium ferrite particles were filtered out, dried and baked at a temperature of 150°C for 5 hours.
- the thus obtained particles had an average particle diameter of 0.08 ⁇ m and a BET specific surface area of 61.1 m 2 /g.
- a coercive force (Hc) was 1,200 Oe and a magnetization (M) was 52.4 emu/g.
- the particles contained 2.5 wt% of zinc.
- Plate-like barium ferrite particles were obtained by the same process as that in Example 13 except that no zinc hydroxide was deposited on the plate-like barium ferrite particle.
- Zinc hydroxide was deposited on the plate-like barium ferrite particles in the same way as in Example 13. The thus obtained plate-like barium ferrite particles were filtered out, dried and baked at a temperature of 500°C for 1.5 hours.
- the thus obtained particles had an average particle diameter of 0.08 ⁇ m and a BET specific surface area of 61/1 m 2 / g.
- a coercive force (Hc) was 1,190 Oe and a magnetization (M) was 53.0 emu/g.
- the particles contained 2.5 wt% of zinc.
- the plate-like barium ferrite particles were obtained in the same way as in Examples 9, 13 to 20 except that no zinc hydroxide was deposited.
- the properties of the particles obtained are shown in Table 3.
Abstract
Description
- The present invention relates to plate-like barium ferrite particles suitable for use in magnetic recording and to a process for producing the same.
- As described, for example, in Japanese Patent Application Laying-Open (KOKAI) No. 55-86103 (1980), ferromagnetic non-acicular particles having a large magnetization, an appropriate coercive force and an appropriate average particle size have recently been demanded as a magnetic recording material and, in particular, as a perpendicular magnetic recording material.
- Generally, barium ferrite particles are known as ferromagnetic non-acicular particles.
- Hitherto, as a process for producing plate-like barium ferrite, a method of autoclaving an aqueous alkaline suspension containing Ba ions and Fe(III) by using an autoclave as a reaction apparatus (this method is hereinafter referred to as "autoclaving") is known.
- With respect to magnetic properties, the magnetization (M) of plate-like barium ferrite particles must be as large as possible, as is described in the specification of Japanese Patent Application Laying-Open (KOKAI) No. 56-149328 (1981); ".... the
- magneto plumbite ferrite which is used as a magnetic recording material is required to have the greatest possible saturation magnetization ....".
- A coercive force of about 300 to 1,500 Oe is generally required, and in order to reduce the coercive force of the produced barium ferrite particles to an appropriate coercive force in the autoclaving process, a method of substituting a part of Fe(III) in ferrite by Ti(IV) and Co(II), or Co(II) and d tivalent metal ions M(II) of Mn, Zn, Ni or the like has been proposed. For example, EP-A-0123445 discloses "plate-like barium ferrite particles which are represented by the formula BaCoxTiyFe12-x-yO19 wherein x and y independently are numbers from 0.1 to 0.5 and which have a BET specific surface area of from 20 to 70 m2/g, an average particle diameter of from 0.05 to 0.3 µm, a magnetization of larger than 30 emu/g in a magnetic field of 7.96 x 105 A m-1 (10 KOe) and a coercive force of from 2.39 x 10 4 to 7.96 x 104 A m-1 (300 to 1,000 Oe)", and "a process for producing plate-like barium ferrite particles represented by the formula:
- The particle size of plate-like barium ferrite particles for use in magnetic recording is required to be as fine as possible, in particular, to be not greater than 0.3 µm.
- This fact is described, for example, in Japanese Patent Application Laying-Open (KOKAI) No. 56-125219 (1981); "... perpendicular magnetic recording is effective in relation to horizontal recording in the region in which the recording wavelength is less than 1 µm. In order to sufficiently record and reproduce in this wavelength region, the crystalline particle diameter of the ferrite is preferably substantially less than 0.3 µm. However, if the particle diameter is about 0.01 µm, the desired coercive force is not exhibited. Therefore, a crystalline particle diameter of 0.01 to 0.3 µm is appropriate".
- In order to reduce noise of a magnetic recording medium, it is necessary that the magnetic particle is as fine as possible and the BET specific surface area is large.
- This fact is described in, for example, "Fig. 3" on lines 23 to 29, p 27, MR 81, Reports of Technical Researches of the Institute of Electronics and Communication Engineers of Japan. Namely, "Fig. 3" shows the relationship between the particle size as well as BET specific surface area and noise level of the particles in acicular maghemite particles with Co deposition.
- As the particle size is made smaller and the BET specific surface area increased, the noise level is linearly lowered. This relationship is the same with plate-like barium ferrite particles.
- Plate-like barium ferrite particles having a large magnetization, an appropriate coercive force, an appropriate particle size and a large BET specific surface area have now been strongly demanded, but it is difficult to obtain plate-like barium ferrite particles having both large BET specific surface area and large magnetization because the magnetization of plate-like barium ferrite particles generally have a tendency to be reduced with the increase in the BET specific surface area.
- The relationship between the BET specific surface area and the magnetization (M) of plate-like barium ferrite particles is obvious from "Fig. 2" and the description "Fig. 2 shows the relationship between the saturation magnetization and the specific surface area in Ba ferrite ... larger in dimension than a single domain.... Saturation magnetization linearly reduces with respect to the BET specific surface area" at p 199 of the Synopses of the Lectures in 7-th Meeting of the Magnetics Society of Japan.
- Actually, although Japanese Patent Application Laying-Open (KOKAI) No. 60-66321 (1985) discloses various plate-like barium ferrite particles having a particular BET specific surface area and a particular magnetization, no plate-like barium ferrite particles which are large in both BET specific surface area and magnetization, in particular, which have both a BET specific surface area of not less than 55 m2/g and a magnetization of not less than 57 emu/g, preferably not less than 60 emu/g, have been yet bbtained.
- The plate-like barium ferrite particles described in the Synopses of the Lectures in 7-th Meeting of the Magnetics Society of Japan and Japanese Patent Application Laying-Open (KOKAI) No. 60-66321 (1985) are obtained by mixing a barium ferrite material with a glass forming material, melting the thus obtained mixture, and rapidly cooling the melt, namely by a so- called glass fusion process. A similar relationship between the BET specific surface area and the magnetization is found with plate-like barium ferrite particles produced by autoclaving.
- The relationship between the BET specific surface area and the magnetization of the plate-like barium ferrite particles produced by autoclaving will be described in more detail as follows.
- In autoclaving, different barium ferrite particles are precipitated depending upon the selected reaction condition. The precipitated particles have ordinarily a hexagonal plate-like configuration, and their particle size, BET specific surface area and magnetic properties are different depending upon the producing condition. It is therefore difficult to obtain plate-like barium ferrite particles having a BET specific surface area of not less than 55 m2/g while maintaining the magnetization at more than 51 emu/g.
- As a method of solving this problem, a method of baking plate-like barium ferrite particles produced from an aqueous solution by autoclaving at a temperature of more than 800°C to improve the magnetization is conventionally known [Japanese Patent Publication No. 60-12973 (1980)].
- In this method, however, the magnetization tends to increase with the rise in baking temperature, and a high temperature of more than 900°C is required in order to obtain a large magnetization, in particular, a magnetization of not less than 57 emu/g, preferably not less than 60 emu/g. In the case of baking at more than 900°C, sintering between the particles is so marked as to bulk, these formed bulk particles being unfavorable as magnetic particles for use in magnetic recording.
- In order to control the coercive force (Hc) of the plate-like barium ferrite particles obtained by baking so as to be less than 1,500 Oe, a large quantity of the above-described coercive force reducing agent must be added, resulting in cause of the magnetization to be lowered. Thus, it is difficult to control the coercive force (Hc) in the range of 300 to 1,500 Oe while maintaining the magnetization at a large value, in particular, at not less than 57 emu/g, preferably not less than 60 emu/g.
- In autoclaving are known a method of adding zinc in the producing reaction of plate-like barium ferrite particles [for example, Japanese Patent Publication Nos. 46-3545 (1971) and 60-12973 (1985)] and a method of coating the surfaces of plate-like barium ferrite particles with the oxide and/or the hydroxide of zinc [Japanese Patent Application Laying-Open (KOKAI)
No. 58-56232 (1983)]. By any of these methods, it is difficult to obtain plate-like barium ferrite particles having a large magnetization (M) and a coercive force (Hc) of 300 to 1,500 Oe. - Thus, the offer of plate-like barium ferrite particles having a large magnetization, an appropriate coercive force and an appropriate average particle size as a magnetic material for magnetic recording, in particular, as a perpendicular magnetic recording material have been strongly demanded.
- As a result of various studies on a process for producing plate-like barium ferrite particles having a large BET specific surface area, a large magnetization and an average particle size of less than 0.1 µm by autoclaving, it has been found that plate-like barium ferrite particles having a BET specific surface area of not less than 55 m2/g, a magnetization (M) of not less than 57 emu/g, preferably not less than 60 emu/g and a coercive force (Hc) of 300 to 1,500 Oe by suspending plate-like barium ferrite particles containing Co and Ti, the atomic ratio of Co to Fe(III) being from 0.02 : 1 to 0.13 : 1 and the molar ratio of Ti to Co being from more than 0 to not more than 0.8, in an aqueous solution containing zinc of pH 4.0 to 12.0 to obtain the plate-like barium ferrite particles deposited with the zinc hydroxide on the surfaces thereof, filtering out and drying the particles, and thereafter baking the particles at a temperature of 600 to 900°C to form a solid solution of zinc on the surfaces of the plate-like barium ferrite particles, and based on the finding the present invention has been attained.
- In a first aspect of the present invention, there is provided plate-like barium ferrite particles with a solid solution of zinc on the surface thereof, which have an average particle diameter of not less than 0.03 µm and less than 0.1 µm, a BET specific surface area of 55 to 80 m2/g, a coercive force of 300 to 1,500 Oe and a magnetization of not less than 57 emu/g in magnetic field of 10 KOe, and which are represented by the following formula (I):
- In a second aspect of the present invention, there is provided a process for producing plate-like barium ferrite particles with a solid solution of zinc on the surface thereof, which are represented by the following formula (I):
which comprises autoclaving at a temperature of from 120 to 330°C an aqueous alkaline suspension of iron hydroxide containing Co(II), Ti(IV) and Ba ions and a molar excess with respect to the total amount of Fe(III), Co(II), Ti(IV) and Ba ions of an alkali metal hydroxide, in said suspension the atomic ratio of the amount of Co to the amount of Fe(III) being from 0.02 : 1 to 0.13 : 1 and the molar ratio of Ti to Co being from more than 0 to not more than 0.8, - suspending the thus obtained plate-like barium ferrite particles containing Co and Ti in an aqueous solution containing zinc of pH 4.0 to 12.0 to deposit the zinc hydroxide on the surface of said plate-like Ba particles containing Co and Ti,
- filtering out and drying the plate-like barium ferrite particles containing Co and Ti deposited with the hydroxide of zinc on the surfaces thereof, and
- baking the particles obtained at a temperature of 600 to 900°C, thereby form a solid solution of zinc on the surface of said plate-like barium ferrite particles.
-
- Figs. 1 and 2 show the relationship between the ratio of addition of Ti to Co (in a molar ratio) in the case of adding 7.86 atom% of Co with respect to Fe(III) and the particle size as well as the BET specific surface area, respectively, of the produced plate-like barium ferrite particles;
- Fig. 3 is electron microphotograph (x 100,000) of the particle structures of the plate-like barium ferrite particles produced from an aqueous solution in Example 1;,
- Fig. 4 is electron microphotograph (x 100,000) of the particle structures of the plate-like barium ferrite particles obtained by baking in Example 9; and
- Fig. 5 shows an X-ray diffraction pattern of the plate-like barium ferrite particles with a solid solution of zinc, obtained in Example 9.
- Plate-like barium ferrite particles suitable for use in magnetic recording according to the present invention, which have an average particle diameter of not less than 0.03 µm and less than 0.1 µm, a BET specific surface area of 55 to 80 m2/g, a coercive force of 300 to 1,500 Oe and a magnetization of not less than 57 emu/g, preferably not less than 60 emu/g, in a magnetic field of 10 KOe, and which are represented by the following formula (I):
- The plate-like barium ferrite particles containing Co and Ti are first produced by adding 2 to 13 atom% of Co compound with respect to Fe(III) and a Ti compound in a molar ratio of 0 < Ti/Co < 0.8 to an aqueous alkaline suspension of iron hydroxide (III) containing Ba ions, and autoclaving the thus obtained aqueous alkaline suspension of iron hydroxide (III) at a temperature ranging from 120 to 330°C. The thus obtained plate-like barium ferrite particles containing Co and Ti is suspended in an aqueous solution containing zinc of pH 4.0 to 12.0 to deposit the zinc hydroxide on the surface of the plate-like barium ferrite particles containing Co and Ti, and after filtering out and drying, the thus obtained plate-like barium ferrite particles are baked at a temperature of 600 to 900°C.
- Namely, the heart of the present invention is characterized in that plate-like barium ferrite particles having an average particle diameter of less than 0.1 um can be produced by adding 2 to 13 atom% of Co compound with respect to Fe(III) and a Ti compound in a molar ratio of 0 < Ti/Co s 0.8 to an aqueous alkaline suspension of iron hydroxide (III), and autoclaving the aqueous alkaline suspension of iron hydroxide (III) at a temperature of 120 to 330°C; the plate-like barium ferrite particles containing Co and Ti are suspended in an aqueous solution containing zinc of pH 4.0 to 12.0, thereby obtaining plate-like barium ferrite particles containing Co and Ti, on which the surface thereof the zinc hydroxide is deposited; and after filtering out and drying, the thus obtained plate-like barium ferrite particles containing Co and Ti are baked at a temperature of 600 to 900°C to form a solid solution of zinc on the surface thereof, thereby enabling the magnetization of the plate-like barium ferrite particles containing Co and Ti to effectively increase at a baking temperature below 900°C while retaining a large BET specific surface area, e.g., a BET specific surface area of not less than 55 m2/g, and as a result the production of plate-like barium ferrite particles containing Co and Ti having a BET specific surface area of not less than 55 m2/g and a magnetization of not less than 57 emu/g, preferably not less than 60 emu/g.
- The present invention will be explained in more detail in the following with reference to some of the experiments carried out by the present inventors.
- Figs. 1 and 2 show the relationship between the ratio of addition (in a molar ratio) of Ti with respect to Co in the case of adding 7.86 atom% of Co to Fe (III), and the particle size and the BET specific surface area, respectively, of the produced plate-like barium ferrite particles.
- As is obvious from Figs. 1 and 2, when Ti is added to Co in a ratio of not greater than 0.8, the particle diameter of the produced plate-like barium ferrite particles is less than 0.1 Um and the BET specific surface area is not less than 65 m2/g in the case of non-baking, and when the ratio of addition of Ti to Co is smaller, the produced plate-like barium ferrite particles become finer.
- A method of adding a Co compound and a Ti compound when producing plate-like barium ferrite particles by autoclaving is conventionally known, as is disclosed in, e.g., Japanese Patent Application Laying-Open (KOKAI) No. 56-149328(1981).
- The purpose of this method, however, is-to reduce a coercive force by adjusting the valence of Fe(III) ions and additives, and therefore it is preferable that the amounts of Co(II) compound and Ti(IV) compound to be added are equimolar. On the other hand, in the present invention, the amounts of Co(II) compound and Ti(IV) compound to be added are different and they are added in order to control the particle size and the BET specific surface area of produced plate-like barium ferrite particles. Accordingly, the process of the present invention is completely different from the conventional process in technical means, objects and effects.
- In the present invention, since it is possible to reduce the amount of a coercive force reducing agent to be added, which will cause the magnetization to be lowered on the basis of the finding that it is possible to effectively increase the magnetization and to lower the coercive force of plate-like barium ferrite particles by forming a solid solution of zinc on the surfaces of the plate-like barium ferrite particles, it is possible to effectively control the coercive force in the range of 300 to 1,500 Oe while retaining a large magnetization.
- The reason why it is possible to effectively increase the magnetization while holding the particle size and a large BET specific surface area and to control the coercive force while maintaining a large magnetization is considered to be that a solid solution of zinc is formed on the surfaces of the plate-like barium ferrite particles, in consideration of the fact that the effects of the present invention cannot be obtained by either a method of adding zinc during production reaction of plate-like barium ferrite particles in autoclaving or a method of coating the surfaces of plate-like barium ferrite particles with the oxide and/or the hydroxide of zinc, as is shown in Comparative Examples.
- In the present invention, in the case where the amount of solid solution of zinc on the surfaces of plate-like barium ferrite particles increases, the magnetization effectively increases and the coercive force reduces.
- The amount of a solid solution of zinc on the surfaces of plate-like barium ferrite particles is controlled by adjusting the pH of the solution at the time of depositing the zinc hydroxide on the surface of the particles and the amount of zinc to be added.
- The amount of deposition of the zinc hydroxide on the surfaces of the particles has a tendency of increasing with the increase in pH, and preferable pH is in the range of 4 to 12 and more preferable pH is in the range of 8 to 10.
- As the Fe(III) salt in the present invention, iron nitride, iron chloride, or the like may be used.
- As the Ba ions in the present invention, barium hydroxide, barium chloride, barium nitride or the like may be used.
- The reaction temperature in autoclaving in the present invention is 120 to 330°C.
- If it is below 120°C, it is difficult to produce plate-like barium ferrite particles.
- Although it is possible to produce plate-like barium ferrite particles even if it exceeds 330°C, the upper limit is determined to be 330°C in consideration of the safety of the apparatus.
- As the Co compound in the present invention, cobalt chloride, cobalt nitride or the like may be used.
- The amount of the Co compound to be added is 2 to 13 atom% with respect to Fe(III).
- If it is less than 2 atom%, it is difficult to produce plate-like barium ferrite particles having a particle diameter of less than 0.1 µm and a BET specific surface area of not less than 65 m2/g in the case of non-baking.
- Although it is possible to produce plate-like barium ferrite particles having a particle diameter of less than 0.1 µm and a BET specific surface area of not less than 65 m2/g in the case of non-baking even if it exceeds 13 atom%, there is no use in adding more Co compound than required.
- The Ti compound used in the present invention includes titanium chloride, titanium oxysulfide and alkali titanium.
- The amount of Ti compound to be added is in the range of 0 < Ti/Co ≦ 0.8 in a molar ratio.
- In the range of 0 < Ti/Co < 0.8, as the amount of Ti to be added becomes smaller, the particle size of the produced plate-like barium ferrite particles becomes smaller and the specific surface area becomes larger. By adjusting the amount of Ti to be added, it is therefore possible to control the particle size and the BET specific surface area so as to have the desired value in the range of a particle diameter of not less than 0.03 µm and less than 0.1 µm and a BET specific surface area of 65 to 150 m2/g in the case of non-baking.
- The entire amount of Co compound and Ti compound to be added is contained in plate-like barium ferrite particles, and accordingly the plate-like barium ferrite particles obtained contains 2 to 13 atom%, preferably 4.0 to 10.0 atom% with respect to Fe, and Ti in the range of 0 < Ti/Co ≦ 0.8, preferably 0.1 < Ti/Co ≦ 0.7 in a molar ratio.
-
- The zinc hydroxide in the present invention is deposited by suspending plate-like barium ferrite particles in an aqueous solution containing zinc of pH 4.0 to 12.0, preferably pH 8 to 10.
- As the zinc compound of the present invention, a halide such as zinc chloride, zinc bromide and zinc iodide; zinc nitride; zinc sulfide; zinc acetate or the like may be used.
- If the pH is less than 4 or more than 12, deposition of zinc is difficult.
- The baking temperature in the present invention is 600 to 900°C, preferably 700 to 850°C.
- If it is below 600°C, a solid solution of zinc on the surfaces of plate-like barium ferrite particles is insufficient.
- If it is above 900°C, since sintering between the particles is too remarkable, it is difficult to obtain plate-like barium ferrite particles having a BET specific surface area of more than 55 m 2 /g.
- The plate-like barium ferrite particles according to the present invention after baking have a BET specific surface area of 55 to 80 m2/g, a coercive force (Hc) of 300 to 1,500 Oe and a magnetization (M) of not less than 57 emu/g, preferably not less than 60 emu/g, in magnetic field of 10 KOe.
- If the BET specific surface area is less than 55 m2/g, it is difficult to reduce noise in a magnetic recording medium, and if it is more than 80 m2/g, dispersion of the particles in a vehicle is difficult.
- In consideration of reduction of noise in a magnetic recording medium and dispersibility in a vehicle, the BET specific surface area is preferably 60 to 75 m2/g.
- -The surfaces of the plate-like barium ferrite particles may be coated with a compound showing an anti-sintering effect such as an Si compound, At compound and P compound before baking.
- The amount of a solid solution of zinc with respect to plate-like barium ferrite particles of the present invention is 0.2 to 5.0 wt%, preferably 0.7 to 4.5 wt%.
- If it is less than 0.2 wt%, it is impossible to sufficiently achieve the object of the present invention.
- Although it is possible to achieve the object of the present invention even if it is more than 5.0 wt%, there is no use in adding a larger amount of zinc than necessary.
- Since the plate-like barium ferrite particles with a solid solution of zinc on the surface thereof according to the present invention, represented by the formula:
- The present invention will now be explained with reference to the following examples and comparative examples.
- The average particle diameter and the specific surface area in each of the examples and comparative examples are represented by the values measured from an electron microphotograph and a BET method, respectively.
- The magnetization (M) and the coercive force (Hc) of the particles were measured in the form of powders in magnetic field of 10 KOe.
- An aqueous alkaline suspension of 14 mol of Fe(NO3)3, 1.2 mol (equivalent to 8.57 atom% with respect to Fe(III)) of Co(NO3)2, 0.2 mol (equivalent to Ti/Co = 0.167 in a molar ratio) of TiCℓ4, 1.40 mol of Ba(OH)2·8H2O and 164 mol of NaOH was charged into an autoclave, heated to 280°C and held at this temperature for 5 hours while being mechanically stirred, to generate brown ferromagnetic precipitates.
- After the suspension was cooled to room temperature, the brown ferromagnetic precipitates were filtered out, washed adequately, and dried.
- The brown ferromagnetic particles were proved by X-ray fluorescence analysis and X-ray diffraction to be barium ferrite particles containing 8.6 atom% of Co with respect to Fe(III) and Ti of Ti/Co = 0.17 in a molar ratio. As is clear from the electron microphotograph (x 100,000) in Fig. 3, they were plate-like particles having an average particle diameter of 0.04 µm and a specific surface area of 90.7·m2/g.
- Various plate-like barium ferrite particles were produced by the same process as that in Example 1 by varying the kinds of ferric salt aqueous solutions and Ba salt aqueous solutions, the kinds and quantities of Co compounds and Ti compounds, and reaction temperature and time.
- The main producing conditions and various properties of the products are shown in Table 1.
- Brown ferromagnetic precipitates were generated in the same way as in Example 2 except that 0.98 mol of zinc chloride, as well as Co and Ti, was added in autoclaving. The precipitates were filtered out, adequately washed and dried.
- The brown ferromagnetic particles were proved by X-ray fluorescence analysis and X-ray diffraction to be barium ferrite particles containing 8.6 atom% of Co with respect to Fe(III) and Ti of Ti/Co = 0.33 in a molar ratio. As a result of the observation of an electron microphotograph, they were proved to be plate-like particles having an average particle diameter of 0.10 µm and a specific surface area of 68.2 m2/g.
- The brown ferromagnetic particles obtained in Example 1 were used as the starting material. 100 g of the starting material was dispersed and mixed in an aqueous solution containing 0.07 mol of zinc chloride, and after the zinc hydroxide was deposited on the surfaces of the particles when the pH of the solution was 6.0, the particles were filtered out, dried and then baked at 800°C for 2.0 hours.
- The particles obtained by baking had an average particle diameter of 0.04 µm and a BET specific surface area of 74.8 m2/g, as is clear from the electron microphotograph (x 100,000) in Fig. 4. With respect to the magnetic properties, a coercive force (Hc) was 710 Oe and a magnetization (M) was 63.9 emu/g.
- As a result of X-ray fluorescence analysis, it was found that the particles contained 8.6 atom% of Co with respect to Fe, Ti of Ti/Co = 0.17 in a molar ratio, and 2.8 wt% of Zn.
- When the plate-like barium ferrite particles were diffracted by an X-ray, only the peaks that represent a magneto plumbite structure were observed, as is clear from Fig. 5, and as a result of chemical analysis of the particles, no zinc oxide or zinc hydroxide was detected which is to be extracted with heating from an alkaline solution. From these facts it was confirmed that a solid solution of Zn had been formed on the surface of the particles. According to X-ray fluorescence analysis, the composition of the thus obtained plate-like barium ferrite particles with a solid solution of zinc is represented by BaO·8.5[(Fe0.909Co0.078Ti0.013)2O2.94].
- Various plate-like barium ferrite particles were produced by the same process as that in Example 9 by varying the kinds of the starting material, and the kinds and quantities of Zn to be added, and heating temperature and time.
- As a result of X-ray diffraction and chemical analysis, it was confirmed that a solid solution of zinc was formed on the surface of the plate-like barium ferrite particles obtained in Examples 10 to 20.
- Plate-like barium ferrite particles with a solid solution of zinc on the surface thereof were obtained by the same process as that in Example 9 except using the plate-like barium ferrite particles obtained in Comparative Example 1 as the starting material.
- The thus obtained particles by baking had an average particle diameter of 0.15 um and a BET specific surface area of 39.3 m2/g. With respect to the magnetic properties, a coercive force (Hc) was 1,290 Oe and a magnetization (M) was 59.1 emu/g.
- As a result of X-ray fluorescence analysis, it was found that the particles contained 1.4 atom% of Co with respect to Fe and 0.5 atom% of Ti with respect to Co, and an amount of a solid solution of zinc thereof was 2.8 wt%.
- Plate-like barium ferrite particles were obtained by the same process as that in Example 13 except using the plate-like barium ferrite particles obtained in Comparative Example 2 as the starting material and depositing no zinc hydroxide.
- The thus obtained particles by baking had an average particle diameter of 0.10 pm and a BET specific surface area of 47.0 m2/g. With respect to the magnetic properties, a coercive force (Hc) was 1,180 Oe and a magnetization (M) was 53.2 emu/g.
- As a result of X-ray fluorescence analysis, it was found that the particles contained 8.6 atom% of Co with respect to Fe, 0.33 atom% of Ti with respect to Co, and 4.4 wt% of zinc.
- Plate-like barium ferrite particles were obtained by the : same process as that in Example 13 except that no zinc hydroxide was deposited on the plate-like barium ferrite particles containing Co and Ti and the baking temperature was 920°C.
- The thus obtained particles by baking had an average particle diameter of 0.18 µm and a BET specific surface area of 18.0 m2/g. With respect to the magnetic properties, a coercive force (Hc) was 1,086 Oe and a magnetization (M) was 57.0 emu/g.
- As a result of X-ray fluorescence analysis, it was found that the particles contained 8.6 atom% of Co with respect to Fe and 0.33 atom% of Ti with respect to Co.
- Plate-like barium ferrite particles were obtained by the same process as that in Example 13 except that no zinc hydroxide was deposited on the plate-like barium ferrite particle.
- Zinc hydroxide was deposited on the plate-like barium ferrite particles
in the same way as in Example 13. The thus obtained plate-like barium ferrite particles were filtered out, dried and baked at a temperature of 150°C for 5 hours. - The thus obtained particles had an average particle diameter of 0.08 µm and a BET specific surface area of 61.1 m2/g. With respect to the magnetic properties, a coercive force (Hc) was 1,200 Oe and a magnetization (M) was 52.4 emu/g.
- As a result of chemical analysis of the particles obtained in Comparative Example 6, the oxide and the hydroxide of zinc were detected which are to be extracted with heating from an alkaline solution. From this fact it was confirmed that zinc existed on the surfaces of the particles in the form of the oxide and the hydroxide of zinc and that a solid solution of zinc was not formed.
- As a result of X-ray fluorescence analysis, it was found that the particles contained 2.5 wt% of zinc.
- Plate-like barium ferrite particles were obtained by the same process as that in Example 13 except that no zinc hydroxide was deposited on the plate-like barium ferrite particle.
- Zinc hydroxide was deposited on the plate-like barium ferrite particles in the same way as in Example 13. The thus obtained plate-like barium ferrite particles were filtered out, dried and baked at a temperature of 500°C for 1.5 hours.
- The thus obtained particles had an average particle diameter of 0.08 µm and a BET specific surface area of 61/1 m 2 /g. With respect to the magnetic properties, a coercive force (Hc) was 1,190 Oe and a magnetization (M) was 53.0 emu/g.
- As a result of chemical analysis of the particles obtained in Comparative Example 7, the oxide and the hydroxide of zinc were detected which are to be extracted with heating from an alkaline solution. From this fact it was confirmed that zinc existed on the surfaces of the particles in the form of the oxide and the hydroxide of zinc and that a solid solution of zinc was not formed.
- As a result of X-ray fluorescence analysis, it was found that the particles contained 2.5 wt% of zinc.
-
Claims (9)
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP61018834A JPS62176918A (en) | 1986-01-29 | 1986-01-29 | Fine platy barium ferrite powder for magnetic recording and its preparation |
JP18834/86 | 1986-01-29 | ||
JP61107457A JPS62265121A (en) | 1986-05-09 | 1986-05-09 | Particulate powder of lamellate ba ferrite and its production |
JP107457/86 | 1986-05-09 |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0232131A2 true EP0232131A2 (en) | 1987-08-12 |
EP0232131A3 EP0232131A3 (en) | 1988-09-21 |
EP0232131B1 EP0232131B1 (en) | 1991-09-18 |
Family
ID=26355566
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP87300780A Expired - Lifetime EP0232132B1 (en) | 1986-01-29 | 1987-01-29 | Plate-like barium ferrite particles suitable for use in magnetic recording and process for producing the same |
EP87300779A Expired - Lifetime EP0232131B1 (en) | 1986-01-29 | 1987-01-29 | Plate-like barium ferrite particles suitable for use in magnetic recording and process for producing the same |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP87300780A Expired - Lifetime EP0232132B1 (en) | 1986-01-29 | 1987-01-29 | Plate-like barium ferrite particles suitable for use in magnetic recording and process for producing the same |
Country Status (4)
Country | Link |
---|---|
US (2) | US4806429A (en) |
EP (2) | EP0232132B1 (en) |
KR (2) | KR870007539A (en) |
DE (2) | DE3773008D1 (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0366370A2 (en) * | 1988-10-24 | 1990-05-02 | Toda Kogyo Corp. | Plate-like composite oxide fine particles containing mainly Ba and Fe, and a process for producing the same |
EP0371384A2 (en) * | 1988-12-01 | 1990-06-06 | Ishihara Sangyo Kaisha, Ltd. | Process for producing magnetic iron oxide particles for magnetic recording |
EP0390594A2 (en) * | 1989-03-31 | 1990-10-03 | Kabushiki Kaisha Toshiba | Magnetic recording medium |
Families Citing this family (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4781981A (en) * | 1986-12-19 | 1988-11-01 | Toda Kogyo Corp. | Plate-like magnetoplumbite ferrite particles for magnetic recording and process for producing the same |
JP2620256B2 (en) * | 1987-10-01 | 1997-06-11 | 日立マクセル株式会社 | Magnetic recording media |
US5358660A (en) * | 1988-01-14 | 1994-10-25 | Showa Denko Kabushiki Kaisha | Magnetic particles for perpendicular magnetic recording |
US5075169A (en) * | 1988-06-08 | 1991-12-24 | Toda Kogyo Corp. | Plate-like composite ferrite particles for magnetic recording and process for producing the same |
EP0349287B1 (en) * | 1988-06-28 | 1995-12-20 | Toda Kogyo Corp. | Plate-like composite ferrite fine particles suitable for use in magnetic recording and process for producing the same |
US5698336A (en) * | 1991-06-28 | 1997-12-16 | Kabushiki Kaisha Toshiba | Magnetic recording medium |
US5378384A (en) * | 1991-09-19 | 1995-01-03 | Minnesota Mining And Manufacturing Company | Process of making hexagonal magnetic ferrite pigment for high density magnetic recording applications |
US5616414A (en) * | 1993-12-28 | 1997-04-01 | Imation Corp. | Hexagonal magnetic ferrite pigment for high density magnetic recording applications |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS5856232A (en) * | 1981-09-30 | 1983-04-02 | Toshiba Corp | Magnetic recording medium |
EP0092394A1 (en) * | 1982-04-19 | 1983-10-26 | Memorex Corporation | Ferro magnetic recording materials |
EP0123445A1 (en) * | 1983-03-26 | 1984-10-31 | Toda Kogyo Corp. | Barium ferrite particles for magnetic recording media |
EP0141558A1 (en) * | 1983-10-12 | 1985-05-15 | Toda Kogyo Corp. | Process of manufacture for barium ferrite particles for magnetic recording media |
Family Cites Families (10)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0072436B1 (en) * | 1981-08-19 | 1986-10-01 | BASF Aktiengesellschaft | Process for the preparation of finely divided ferrite powder |
JPS5941806A (en) * | 1982-08-31 | 1984-03-08 | Toda Kogyo Corp | Manufacture of tabular ba ferrite particle powder for magnetic recording |
AU558199B2 (en) * | 1982-09-16 | 1987-01-22 | Ishihara Sangyo Kaisha Ltd. | Production of magnetic powder |
JPS59161002A (en) * | 1983-02-05 | 1984-09-11 | Toda Kogyo Corp | Laminar ba ferrite fine particle for magnetic recording and manufacture thereof |
JPS6070518A (en) * | 1983-09-28 | 1985-04-22 | Toshiba Corp | Magnetic recording medium |
JPS6095902A (en) * | 1983-10-31 | 1985-05-29 | Toda Kogyo Corp | Manufacture of tabular ba ferrite corpuscular powder for magnetic recording |
JPS60137002A (en) * | 1983-12-26 | 1985-07-20 | Toda Kogyo Corp | Manufacture of tabular ba ferrite fine particle powder for magnetic recording |
KR900000429B1 (en) * | 1984-05-31 | 1990-01-30 | 도다 교오교오 가부시끼가이샤 | Barium ferrite particles for magnetic recording media |
US4683167A (en) * | 1984-06-25 | 1987-07-28 | Ampex Corporation | Magnetic iron oxide pigment and recording media |
IT1199501B (en) * | 1984-10-12 | 1988-12-30 | Consiglio Nazionale Ricerche | METHOD FOR THE PREPARATION OF FINE POWDERS OF HEXAGONAL FERRITS, IN PARTICULAR FOR MAGNETIC REGISTRATION |
-
1987
- 1987-01-29 DE DE8787300779T patent/DE3773008D1/en not_active Expired - Lifetime
- 1987-01-29 US US07/008,466 patent/US4806429A/en not_active Expired - Lifetime
- 1987-01-29 US US07/008,439 patent/US4851292A/en not_active Expired - Fee Related
- 1987-01-29 EP EP87300780A patent/EP0232132B1/en not_active Expired - Lifetime
- 1987-01-29 DE DE8787300780T patent/DE3773403D1/en not_active Expired - Lifetime
- 1987-01-29 EP EP87300779A patent/EP0232131B1/en not_active Expired - Lifetime
- 1987-01-30 KR KR870000795A patent/KR870007539A/en not_active Application Discontinuation
- 1987-01-30 KR KR870000794A patent/KR870007538A/en not_active Application Discontinuation
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS5856232A (en) * | 1981-09-30 | 1983-04-02 | Toshiba Corp | Magnetic recording medium |
EP0092394A1 (en) * | 1982-04-19 | 1983-10-26 | Memorex Corporation | Ferro magnetic recording materials |
EP0123445A1 (en) * | 1983-03-26 | 1984-10-31 | Toda Kogyo Corp. | Barium ferrite particles for magnetic recording media |
EP0141558A1 (en) * | 1983-10-12 | 1985-05-15 | Toda Kogyo Corp. | Process of manufacture for barium ferrite particles for magnetic recording media |
Non-Patent Citations (1)
Title |
---|
PATENT ABSTRACTS OF JAPAN, vol. 7, no. 142 (P-205)[1287], 22nd June 1983; & JP-A-58 56 232 (TOKYO SHIBAURA DENKI K.K.) 02-04-1983 * |
Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0366370A2 (en) * | 1988-10-24 | 1990-05-02 | Toda Kogyo Corp. | Plate-like composite oxide fine particles containing mainly Ba and Fe, and a process for producing the same |
EP0366370A3 (en) * | 1988-10-24 | 1991-04-03 | Toda Kogyo Corp. | Plate-like composite oxide fine particles containing mainly ba and fe, and a process for producing the same |
EP0371384A2 (en) * | 1988-12-01 | 1990-06-06 | Ishihara Sangyo Kaisha, Ltd. | Process for producing magnetic iron oxide particles for magnetic recording |
EP0371384B1 (en) * | 1988-12-01 | 1995-06-21 | Ishihara Sangyo Kaisha, Ltd. | Process for producing magnetic iron oxide particles for magnetic recording |
EP0390594A2 (en) * | 1989-03-31 | 1990-10-03 | Kabushiki Kaisha Toshiba | Magnetic recording medium |
EP0390594A3 (en) * | 1989-03-31 | 1991-01-16 | Kabushiki Kaisha Toshiba | Magnetic recording medium |
Also Published As
Publication number | Publication date |
---|---|
DE3773403D1 (en) | 1991-11-07 |
EP0232132A2 (en) | 1987-08-12 |
KR870007539A (en) | 1987-08-20 |
EP0232132B1 (en) | 1991-10-02 |
US4851292A (en) | 1989-07-25 |
KR870007538A (en) | 1987-08-20 |
US4806429A (en) | 1989-02-21 |
DE3773008D1 (en) | 1991-10-24 |
EP0232132A3 (en) | 1988-09-21 |
EP0232131B1 (en) | 1991-09-18 |
EP0232131A3 (en) | 1988-09-21 |
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